Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disease affecting males almost exclusively. WAS consists of 3 main features: thrombocytopenia with resultant bleeding / bruising, immunodeficiencies including both B-cell and T-cell abnormalities with resultant fungal, viral, and bacterial infections, and severe atopic dermatitis (usually begins in the first few months of life). The most common presenting symptoms of easy bruising, petechiae, and purpura are often noted at birth and are the manifestations of platelet abnormalities which include thrombocytopenia and abnormally small and dysfunctional platelets. These platelet abnormalities can lead to bloody diarrhea.

Viral (warts, herpes, and molluscum) and bacterial infections occur frequently in infancy and early childhood, most commonly bacterial otitis media, sinusitis, pneumonias, impetigo, cellulitis, and abscesses. Furthermore, WAS patients have a high prevalence of food allergies, asthma, and urticaria. Up to 70% of patients are also found to have autoimmune disorders, including cytopenias, arthritis, and vasculitis. Milder forms of WAS have been described that do not involve the typical immunodeficiencies.

WAS may be further complicated by the development of lymphoreticular malignancies (especially non-Hodgkin lymphoma and Epstein-Barr virus-induced lymphomas) and leukemia in childhood.

Females may have the syndrome due to nonrandom X-chromosome inactivation.